Clip-type tensioners, as they are known, have been used in the past as chain tensioners. A clip-type tensioner consists of a housing, a piston which is slidably supported in a hole of the housing, a spring for urging the piston so as to protrude from the hole, and a ratchet mechanism. The ratchet mechanism has a number of rack teeth on the outer periphery of the piston, a clip which engages with the rack teeth, and a recess on the inner peripheral surface of the housing. One example is shown in FIG. 1 of Japanese Unexamined Patent Application Publication 2005-98420. The recess on the inner peripheral surface of the housing has a front end face which comes into contact with the clip when the piston advances, allowing the piston to advance, and a rear end face (seat face) which comes into contact with the clip when the piston retracts, thereby holding the clip between the rack teeth and restricting retraction of the piston.
When slack is produced in the chain during operation, the piston advances toward the chain under the elastic repelling force of the spring and protrudes outside the housing The clip which has engaged with the rack teeth on the outer periphery of the piston comes into contact with the front end face of the recess at this point, which means that the piston is allowed to advance. On the other hand, when tension in the chain increases, the excessive pressing force from the chain causes the piston to retract, pushing it into the housing The clip which has engaged with the rack teeth on the outer periphery of the piston comes into contact with the rear end face of the recess at this point, which means that retraction of the piston is restricted.
However, with the conventional clip-type tensioner described above, when the piston has been pushed into the housing, the clip collides with the rear end face of the recess, causing the clip to exert an excessive pressing force on the rear end face of the recess. Consequently, the rear end face of the recess is worn with repeated usage.